Study On The Design And Numerical Simulation Of Pile Anchor Support For A Foundation Pit In Changchun

Since the 21 st century,with the accelerating process of urbanization in China,the usable area of land resources has become increasingly limited,and the siphon of population and resources by central cities has brought great pressure to urban housing and transportation.In order to expand the increasingly saturated living space,high-rise buildings and underground projects are mushrooming.Foundation pit engineering as the basis of high-rise buildings and all kinds of civil air defence underground engineering,the excavation and supporting the related theory and technology continues to attract the attention of people,how to ensure safety,stability and low cost under the premise of the environment according to the different geological conditions and construction of retaining structure optimization become very necessary engineering issues.Taking a foundation pit project in Changchun City as the research object,this paper discusses the necessity of pile-anchor support in this project by comparing a variety of support schemes.By means of design checking calculation and numerical simulation combined with foundation pit monitoring,dynamic analysis is carried out in different construction stages.The conclusions drawn are of certain reference value to similar projects in this region.The main contents of the study are as follows:(1)The development current situation of foundation pit engineering and pileanchor retaining structure at home and abroad is summarized in detail.(2)The structure and failure types of pile-anchor support system are summarized,and the calculation principle of earth pressure and supporting structure is expounded and analyzed.(3)The design scheme was issued according to the geological condition of the site,and the stability of the foundation pit support was checked by using Lizheng software,and the results were in line with the standard.(4)Midas GTS finite element software is introduced.The 2-2 area on the east side of the foundation pit is taken as the research object for numerical simulation.The results show that the maximum horizontal displacement of pile appears at the depth of H0.6～0.8 times.The surrounding surface settlement is positively correlated with the excavation depth,and the maximum settlement occurs at a depth about 0.4 times the horizontal distance from the pit edge.The position of the maximum bending moment and the maximum shear force of the supporting pile is consistent,and both reach the maximum value when the last step of excavation is completed.The maximum axial force of the anchor cable appears at the bottom of the anchor cable.The axial force of the anchor cable is smaller than that of the free section,and the distribution of the axial force in the free section is more uniform.Comparing the simulated data with the monitoring data,it is found that the error is small,indicating that the numerical simulation is relatively reliable.(5)The consequences indicate that increasing the pile diameter or reducing the Angle of the anchor cable can reduce the displacement of the supporting structure to some extent.However,after weighing the advantages and disadvantages of safety and economy,it is reasonable to choose the Angle of 0.8m anchor cable as 15° on the slope of the supporting pile.